基于FE-SEM大视域拼接技术定量表征致密砂岩储集空间——以泌阳凹陷核桃园组为例

Quantitative characterization of reservoir space of tight sandstones based on a large-view FE-SEM splicing technology: a case study on the Hetaoyuan Formation in Biyang sag

通过铸体薄片与场发射扫描电镜(FE-SEM),将泌阳凹陷核桃园组三段致密砂岩储层储集空间分为粒间孔、粒内孔、裂缝三大类,以粒间孔与粒内孔为主,再根据矿物组成将粒间孔划分为石英粒间孔、长石粒间孔、石英颗粒边缘孔、长石颗粒边缘孔、碳酸盐矿物粒间孔,将粒内孔分为石英溶蚀孔、长石溶蚀孔、碳酸盐矿物粒内孔、黏土矿物晶间孔等,粒内孔在中部3023~3035m层段相对发育。基于高分辨率FE-SEM大视域拼接技术,将上述所细分孔隙类型进行了定量标定。研究结果表明,泌阳凹陷核三段致密砂岩储层面孔率为3.75%,其中粒间孔与粒内孔面孔率分别为2.35%和1.38%,裂缝面孔率仅为0.02%。不同的储集空间类型中,孔隙直径的分布有所差异,其中石英粒间孔与长石粒间孔均以50~100nm的直径所占比例最大,占比分别为42.4%与30%,石英颗粒边缘孔与长石颗粒边缘孔则以直径100~200nm的居多,均占30%;粒间孔中,尽管直径大于1000nm的孔隙所占数量比例均小于6%,但其对孔隙面积的贡献非常大,其中直径大于1000nm的石英粒间孔与长石粒间孔均占其总孔隙面积的95%以上;各类型粒内孔均以直径100~200nm的孔隙为主,石英溶蚀孔及长石溶蚀孔在孔隙面积分布上与其他粒内孔有所差异,其孔隙面积以直径200~500nm的孔隙略具优势,所占比例均大于35%。

Based on casting thin sections and FE-SEM（field emission scanning electron microscope）, the reservoir space of tight sandstone in the 3 rd member of the Hetaoyuan Formation in the Biyang sag is divided into three types, including intergranular pores, intragranular pores and fractures. The former two, intergranular pores and intragranular pores, are primary reservoir space. According to the mineral composition, the intergranular pores are divided into quartz and feldspar intergranular pores, quartz and feldspar grain-boundary pores, and intergranular carbonate pores; the intragranular pores are divided into dissolved quartz and feldspar pores, intragranular carbonate pores and intercrystalline clay pores, which are relatively developed between 3023 m and 3035 m. Theses pore types are quantitatively calibrated based on a highresolution and large-view FE-SEM splicing technology. The results show that the surface porosity of the tight sandstone in the 3 rd member of Hetaoyuan Formation is 3.75%, of which intergranular pores, intragranular pores and fractures account for 2.35%, 1.38% and 0.02%, respectively. In various types of reservoirs, the pore diameters have some differences, the intergranular pores of quartz and feldspar mainly ranging from 50 to 100 nm account for 42.4% and 30% respectively, and the grain-boundary quartz and feldspar pores mostly from 100 to 200 nm account for 30% each. Although the intergranular pores larger than 1000 nm account for less than 6%, they contribute more to total pore volume, of which the intergranular quartz and feldspar pores larger than 1000 nm account for 95% of each pore volume. The intragranular pores in the range of 100 to 200 nm are dominant; quartz and feldspar dissolution pores are slight different from other types, and the pores between 200 and 500 nm are dominant, and account for more than 35% of each total pore volume.